Method suitable for middle denitration of ultrafine-particle hematite pellets

Abstract

The invention belongs to the technical field of hematite denitration, and particularly relates to a method suitable for middle denitration of superfine hematite pellets, which comprises the following steps: (1) controlling the high-point temperature of flue gas of a catalyst layer of a denitration tower to be 390-400 DEG C; (2) the high-point temperature of a preheating second-section air bellow of the chain grate machine is controlled to be 550-590 DEG C; (3) increasing the air volume of a backheating fan; (4) the temperature of an inlet of a main exhaust fan is controlled to be 140-150 DEG C, and the negative pressure of a kiln tail is controlled to be 220-260 Pa; (5) increasing the distribution thickness of the south side and the north side of the chain grate machine, controlling the distribution thickness to be 190 + / -10mm, and controlling the thickness difference between the south side and the north side to be + / -5mm; (6) a first air bellow branch pipe of the first preheating section of the chain grate machine is connected to a regenerative horizontal pipe of the second preheating section of the chain grate machine; (7) adjusting a float flowmeter according to the nitrogen oxide content of the original flue gas at the inlet of the south-north denitration tower, increasing the ammonia spraying amount of the south-side denitration tower, and reducing the ammonia spraying amount of the north-side denitration tower; and (8) the emission of nitric oxide is controlled in a centralized control mode, and the emission is controlled to be 20-30 mg / Nm. By adopting the method, ammonia escape is reduced, the temperatures of the first preheating section and the second preheating section are controlled, and the denitration efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of hematite denitrification, and in particular relates to a method suitable for denitrification in the middle of ultrafine hematite pellets. Background Art

[0002] The raw material for pellet production of Lanxian Mining Company of Taigang Group is ultrafine hematite, and the fuel is pulverized coal. It is burned in a rotary kiln and a chain grate for heating. About 8 tons of coal are burned per hour, and the amount of fuel-type NOx generated is large. At the same time, due to the high temperature of the hematite pellet system, a large amount of thermal NOx is generated, so the system denitrification pressure is large. The traditional denitrification system adopts a medium-high temperature SCR denitrification system with a reaction temperature of 280-400℃, a large reaction range, and the reaction efficiency increases with the increase of temperature. Due to the low flue gas temperature, traditional post-denitrification requires external heat supplement to increase the reaction temperature to 320℃, and the denitrification efficiency reaches 85%, but the denitrification efficiency is low; process flow: preheating stage II → multi-tube dust removal → middle SCR denitrification → heat recovery → extraction stage → main exhaust fan → wet desulfurization system → wet electrostatic precipitator → chimney emission, the operational difficulties of the middle SCR denitrification: (1) The flue gas temperature is high and the catalyst layer operation cycle is reduced; (2) During the roasting process of hematite pellets, a large amount of coal is injected, and the nitrogen oxide content in the original flue gas is high and fluctuates greatly; (3) After the temperature of the second-stage preheating bellows decreases, the preheating effect of the balls entering the kiln is affected, resulting in a large amount of powder; (4) The hood temperature in the drying section is low, which affects the dehydration and drying effect of the green balls. After entering the preheating section, a large number of burst balls are produced; (5) After the float flowmeter is stuck, the ammonia injection amount of some ammonia injection branches cannot be adjusted; (6) The thickness of the grate material layer varies greatly and fluctuates frequently, and the wind speed on both sides varies greatly; (7) The middle denitrification only removes NOx from the second stage flue gas preheated by the chain grate, which is partial flue gas denitrification. The NOx in the first stage flue gas preheated is directly discharged without passing through the denitrification system, and the NOx emission value fluctuates greatly. Summary of the invention

[0003] The purpose of the present invention is to provide a method suitable for denitrification in the middle of ultrafine hematite pellets, so as to solve the operational difficulties of the above-mentioned middle SCR denitrification.

[0004] In order to achieve the above object, the present invention adopts the following technical scheme: A method for denitrification in the middle of ultrafine hematite pellets, comprising the following contents: (1) Control the flue gas high point temperature of the catalyst layer of the denitrification tower to 390-400℃, balancing the preheating effect of the second stage and the denitrification reaction temperature; (2) Reduce the temperature control range of the second-stage wind box of the chain grate preheating machine, control the high point temperature of the wind box at 550-590℃, and stabilize the original flue gas temperature at the inlet of the denitrification tower; (3) Increase the air volume of the heat recovery fan, speed up the original flue gas flow rate, and improve the denitrification reaction efficiency; (4) Control the inlet temperature of the main exhaust fan at 140-150℃, the negative pressure at the kiln tail at 220-260Pa, match the air volume of the main exhaust fan and two heat recovery fans, and stabilize the inlet flue gas velocity, flow rate, and flow field; (5) Chain grate cloth modification: increase the cloth thickness on the north and south sides, keep the cloth thickness of the chain grate at 190±10mm, control the north-south material thickness difference at ±5mm, make the grate bed material thickness uniform, prevent short circuit of hot air in thin material layer, and avoid sudden temperature fluctuation of denitrification system; (6) Chain grate bellows modification: connect the first bellows branch pipe of the chain grate preheating stage 1 to the horizontal heat recovery pipe of the chain grate preheating stage 2, and adjust the temperature of the preheating stage 1 and preheating stage 2; (7) Float flowmeter regional adjustment and transformation: According to the nitrogen oxide content of the original flue gas at the inlet of the north and south denitrification towers, the float flowmeter is adjusted to increase the ammonia injection amount of the south denitrification tower and reduce the ammonia injection amount of the north denitrification tower; (8) Centrally control nitrogen oxide emissions, control the emission content conversion value at 20-30mg / Nm³, and adjust the frequency of the ammonia delivery pump in time.

[0005] Preferably, the wind speed of the heat recovery fan in (3) is controlled at 0.8-1.0 m / s to ensure the material preheating effect and stabilize the original flue gas flow rate.

[0006] Preferably, the (5) also includes increasing the length of the swing arm of the swing mechanism by 0.2 mm, extending the swing arm travel, adding five variable frequency rollers to the large roller screen, and rectifying the material in sections; the upper edge height of the material sliding plate is 120 mm.

[0007] Preferably, in (7), a plurality of ammonia spray branch pipes are respectively arranged at the north and south inlet flues of the denitrification tower, and a set of float flow regulation system is added to each ammonia spray branch pipe. Each ammonia spray branch pipe is provided with a plurality of nozzles. Ammonia water passes through a float flowmeter and then enters the denitrification tower through the nozzle. The float flowmeters on both sides accurately control the single nozzle flow of each nozzle in the north and south to achieve a rectification effect. The flow of the float flowmeter is adjusted according to the distribution of the flue gas flow field and the flue gas flow velocity in the denitrification tower to maximize the reaction rate of the sprayed ammonia and reduce ammonia escape.

[0008] Compared with the prior art, the present invention has the following beneficial effects: (1) By controlling the high point temperature of the flue gas in the denitration catalyst layer and reducing the temperature control range of the second-stage wind box of the chain grate preheating, the flue gas temperature is prevented from being too high and the operation cycle of the catalyst layer is increased; (2) By increasing the air volume of the heat recovery fan, the reaction rate of the ejected ammonia is increased, ammonia escape is reduced, and the emission of nitrogen oxides is controlled by centralized control to avoid direct emission of NOx in the flue gas without passing through the denitrification system; (3) By controlling the inlet temperature of the main exhaust fan and the negative pressure at the kiln tail, the coal injection amount is large during the roasting process, the nitrogen oxide content in the original flue gas is high, and the fluctuation is reduced; (4) By adjusting the cloth thickness on both sides of the chain grate, the thickness difference can be reduced to prevent large changes in wind speed on both sides and short circuit of hot air in the thin material layer, so as to avoid sudden temperature fluctuations in the denitrification system, which will cause the temperature of the smoke hood in the drying section to be low, affecting the dehydration and drying effect of the green pellets; (5) By connecting the first wind box branch pipe of the chain grate preheating stage 1 to the heat recovery horizontal pipe of the chain grate preheating stage 2, the temperature of the wind box of the preheating stage 2 is prevented from decreasing and affecting the preheating effect of the balls entering the kiln; (6) An ammonia injection branch pipe is provided at each of the north and south inlet flues of the denitrification tower. A float flow control system is added to each ammonia injection branch pipe. Each ammonia injection branch pipe is provided with 5 nozzles. Ammonia water passes through the float flowmeter and then enters the denitrification tower through the nozzle. The float flowmeters on both sides can accurately control the flow of each nozzle of the 5 nozzles in the north and south to avoid the ammonia injection amount of some ammonia injection branches cannot be adjusted after the float flowmeter is stuck. DETAILED DESCRIPTION

[0009] The technical solution of the present invention is described clearly and completely below in conjunction with the embodiments.

[0010] The method for denitrification in the middle of a hematite pellet chain loop production line includes the following contents: (1) Control the flue gas high point temperature of the catalyst layer of the denitrification tower to 390-400℃, balancing the preheating effect of the second stage and the denitrification reaction temperature; (2) Reduce the temperature control range of the second-stage wind box of the chain grate preheating machine, control the high point temperature of the wind box at 550-590℃, and stabilize the original flue gas temperature at the inlet of the denitrification tower; (3) Increase the air volume of the heat recovery fan and control the wind speed at 0.8-1.0m / s to speed up the original flue gas flow rate and improve the denitrification reaction efficiency; (4) Control the inlet temperature of the main exhaust fan at 140-150℃, the negative pressure at the kiln tail at 220-260Pa, match the air volume of the main exhaust fan and two heat recovery fans, and stabilize the inlet flue gas velocity, flow rate, and flow field; (5) Chain grate cloth modification: the length of the swing arm of the swing mechanism is increased by 0.2mm, and the stroke of the swing arm is extended; five variable frequency rollers are added to the large roller screen to rectify the material in sections; the upper edge height of the chute is 120mm; the cloth thickness on the north and south sides is increased, the cloth thickness of the chain grate is maintained at 190±10mm, and the thickness difference between the north and south is controlled at ±5mm, so as to make the grate bed material thickness uniform, prevent the short circuit of hot air in the thin material layer, and avoid sudden temperature fluctuations in the denitrification system; (6) Chain grate wind box transformation: The chain grate preheating section 2 is 27m long and consists of 9 wind boxes. The preheating section 1 is 15m long and consists of 6 wind boxes, including 3 2m wind boxes. The temperature range of the preheating section 2 wind boxes is 300-590℃, with an average temperature of 450-470℃. The average inlet temperature of the denitrification tower is 420-430℃, and the cold air valve needs to be opened frequently to cool down. The temperature of the last wind box in the preheating section is 280-330℃. Its branch pipe is transformed and connected to the reheating horizontal pipe in the preheating section 2 to reduce the inlet temperature of the reheating fan. The inlet temperature of the denitrification tower is reduced to 390-400℃, which meets the optimal reaction efficiency temperature of the catalyst in the denitrification tower. (7) Float flowmeter regional adjustment transformation: 5 ammonia injection branch pipes are set at the north and south inlet flues of the denitrification tower, and a float flow adjustment system is added to each ammonia injection branch pipe. Each ammonia injection branch pipe is equipped with 3 nozzles. Ammonia water passes through the float flowmeter and then enters the denitrification tower through the nozzle. The float flowmeters on both sides accurately control the single nozzle flow of each nozzle in the north and south to achieve a rectification effect. The flow of the float flowmeter is adjusted according to the distribution of the flue gas flow field and the flue gas flow rate in the denitrification tower to maximize the reaction rate of the sprayed ammonia and reduce ammonia escape; (8) Centrally control nitrogen oxide emissions and keep them within 20-30 mg / Nm³ (converted value), and adjust the frequency of the ammonia delivery pump in a timely manner.

[0011] Adjust the temperature of the first and second preheating stages to stabilize the flue gas temperature entering the denitrification tower at 380°C, reaching the optimal reaction temperature, and the denitrification reaction efficiency is greater than 93%.

[0012] The hematite pellet chain loop production line is perfectly matched with the central denitrification method. From June 2023 to date, the flue gas emission compliance rate has been 100%, the average NOx emission value is 24mg / m³, and the average NOx emission is 0.32t / d; the heating coal is reduced by 1,200 tons / year, and the cost is reduced by 8.05 million / year; the rotary kiln production cycle can be stabilized at more than 50 days, the ammonia consumption index is lower than the lowest level in the industry, and nitrogen oxide regulation can be precisely adjusted.

Claims

1. A method for denitrification of the middle part of ultrafine hematite pellets, characterized in that: Includes the following: (1) Control the flue gas high point temperature of the catalyst layer of the denitrification tower to 390-400℃, and balance the preheating effect of the second stage and the denitrification reaction temperature; (2) Narrow the temperature control range of the second-stage wind box of the chain grate preheating machine, control the high point temperature of the wind box at 550-590℃, and stabilize the original flue gas temperature at the denitrification tower inlet; (3) Increase the air volume of the heat recovery fan to speed up the flow rate of the original flue gas; (4) Control the main exhaust fan inlet temperature at 140-150℃, the kiln tail negative pressure at 220-260Pa, and match the air volume of the main exhaust fan and two heat recovery fans; (5) Chain grate fabric modification: increase the fabric thickness on the north and south sides, maintain the fabric thickness of the chain grate at 190±10mm, control the thickness difference between the north and south sides at ±5mm, and make the grate bed material thickness uniform; (6) Chain grate bellows modification: connect the first bellows branch pipe of the chain grate preheating stage 1 to the heat recovery horizontal pipe of the chain grate preheating stage 2, and adjust the temperature of the preheating stage 1 and preheating stage 2; (7) Float flowmeter regional adjustment and transformation: According to the nitrogen oxide content of the original flue gas at the inlet of the north and south denitrification towers, the float flowmeter is adjusted to increase the ammonia injection amount of the south denitrification tower and reduce the ammonia injection amount of the north denitrification tower; (8) Centrally control nitrogen oxide emissions, control the emission content conversion value at 20-30mg / Nm³, and adjust the ammonia delivery pump frequency in a timely manner.

2. The method for denitrification of the middle portion of ultrafine hematite pellets according to claim 1, characterized in that: The wind speed of the heat recovery fan in (3) is controlled at 0.8-1.0m / s.

3. A method for denitrification in the middle of ultrafine hematite pellets according to any one of claims 1 or 2, characterized in that: Said (5) also includes the swing mechanism swing arm swing rod length increased by 0.2mm, extending the swing arm travel, adding five variable frequency rollers to the large roller screen, and rectifying the material in sections; the upper edge height of the material chute is 120mm.

4. The method for denitrification of the middle portion of ultrafine hematite pellets according to claim 3, characterized in that: In the above (7), a plurality of ammonia spraying branch pipes are respectively provided at the north and south inlet flues of the denitrification tower, and a set of float flow regulating system is added to each ammonia spraying branch pipe. A plurality of nozzles are provided on each ammonia spraying branch pipe. Ammonia water passes through a float flow meter and then enters the denitrification tower through the nozzle. The float flow meters on both sides accurately control the flow rate of each nozzle in the north and south. The flow rate of the float flow meter is adjusted according to the distribution of the flue gas flow field and the flue gas flow velocity in the denitrification tower, so as to maximize the reaction rate of the sprayed ammonia and reduce ammonia escape.